The invention relates to an apparatus for the recording or for the reproduction of information with a drive system for a scanning device which is formed by a toothed rack arrangement driven by means of a special worm-gear mechanism. The drive system is provided for an apparatus for the recording or an apparatus for the reproduction of information which uses a scanning device to read or store information or data in one or more tracks of a recording medium. The recording medium may be, for example, a compact disc, known as CD, a digital versatile disc, known as DVD, a CD-ROM or DVD-ROM or an erasable CD or DVD or else a magneto-optical or other recording medium.
Apparatuses for the recording or for the reproduction of information or data in one or more tracks of a recording medium are generally known. Data or information are read from the recording medium or recorded on the recording medium by means of a scanning device, which is also referred to as xe2x80x9cpick-upxe2x80x9d and is arranged on a carriage which can be moved at an inclination or perpendicularly with respect to the recording track of the recording medium. In order to be able to access different points on the recording medium with high accuracy and speed and with a short access time, a toothed rack arrangement is generally provided on the carriage carrying the scanning device, which toothed rack arrangement is driven by an electric motor via a gearwheel mechanism. In order to compensate for tooth play, the toothed rack arrangement comprises two toothed racks which are braced with respect to one another by means of a spring, and either a pinion or a worm wheel for driving the gearwheel mechanism -is provided on the shaft of the electric motor. The gearing is designed to be self-locking in order to prevent alterations to the position of the scanning device when the drive is switched off or the electric motor is switched off. In accordance with the requirements made of a drive system for scanning devices in respect of positioning accuracy, speed and self-locking, use is made of gearwheel mechanisms driven by a pinion and having high transmission by means of a plurality of gearwheels or worm-gear mechanisms which comprise a worm and a worm wheel which is designed as a helical toothed spur wheel and is arranged on a common axle with a gearwheel driving the toothed rack arrangement. The toothed rack arrangement and the gearwheel driving the toothed rack arrangement are provided with straight toothing, in order to avoid displacements of the scanning device in the direction of the recording medium, such as the focused direction in the case of an optical recording medium, during tracking or track jumping and in the event of a change in the drive direction. For this reason, the toothed rack arrangement cannot be driven directly with a worm. Known worm-gear drives for scanning devices therefore use, in principle, a worm wheel driven by a worm and a gearwheel for driving the toothed rack arrangement. The worm wheel is helically toothed, in contrast to the gearwheel, and the axes of worm and worm wheel are arranged perpendicularly to one another. Drives of this type satisfy the requirements in respect of a short access time, little outlay and high positioning accuracy only to an inadequate extent, since resiliently braced toothed rack arrangements enable reliable positioning only at low speed. A change in the drive direction increases the access time. Numerous gearwheels as well as special gearing toothed wheels, such as, for example, in the case of a worm-gear mechanism which is as free from play as possible, require a high outlay. However, it is an advantage of the worm-gear mechanism that self-locking is achieved with a comparatively smaller number of gearwheels.
The object of the invention is to provide a drive system for a scanning device which requires little outlay and satisfies the requirements in respect of high positioning accuracy, short access time and self-locking.
This object is achieved by means of the features of the invention specified in the independent claim. Advantageous developments of the invention are specified in dependent claims.
One aspect of the invention is to configure a drive system for a scanning device in such a way that a high positioning accuracy and speed in the course of accessing different points on the recording medium as well as self-locking of the drive system are ensured with little outlay.
These requirements are met by means of a drive system which can be formed with just a one-piece toothed rack and has the advantageous properties of a worm-gear mechanism even though no worm wheel or helically toothed gearwheel is provided.
The drive system for a scanning device in an apparatus for the recording or for the reproduction of information is constructed in such a way that the toothed rack arrangement and the worm are arranged in engagement with just a single gearwheel. The gearwheel is a straight-toothed intermediate gearwheel and the worm which drives the toothed rack arrangement via the gearwheel is arranged at an angle with respect to the gearwheel, which angle corresponds to the lead of the said worm. By virtue of the inclined position of the worm, a straight-toothed gearwheel is advantageously brought into engagement with the worm, with the result that advantageous properties of a worm-gear mechanism are preserved and a helically toothed gearwheel is obviated. The worm is preferably a multi-start worm arranged on a shaft having counterbearings in the axial direction, in order to ensure that the scanning device immediately follows a change in the direction of the drive.
To that end, a first counterbearing is preferably formed by a driving electric motor and a second counterbearing is formed by a limiting means which limits axial play of the shaft of the electric motor. The worm is arranged on the shaft of the electric motor. The shaft with the worm and the electric motor are preferably arranged parallel to the toothed rack arrangement and at an angle with respect to the gearwheel with respect to the toothed rack arrangement, which angle corresponds to the lead of the worm. As a result, a first engagement of the gearwheel with the toothed rack arrangement and a second engagement of the gearwheel with the worm are situated opposite one another. As a result, the gearwheel driving the toothed rack arrangement is additionally supported by the worm against the toothed rack arrangement, thereby preventing the gearwheel from being forced away from the toothed rack and avoiding a corresponding slip. Compared with a toothed rack arrangement driven by a spur wheel, the inventive drive system with the gearwheel provided as intermediate gearwheel has improved robustness and a smaller degree of play. The smaller degree of play also results, inter alia, from the reduced number of gearwheels of the drive system and it is possible to use a toothed rack arrangement formed by a one-piece toothed rack, whereby the play in the event of a change in the drive direction is further reduced and the access time to different points on the recording medium is shortened.
By virtue of the engagement of the worm in the gearwheel provided as intermediate gearwheel being arranged oppositely with respect to the toothed rack, the tooth play is reduced in such a way that it is possible to use just a one-piece toothed rack. Additional means for compensating for tooth play, such as a toothed rack arrangement comprising resiliently braced toothed racks, are not necessary. This may be ascribed, inter alia, to the fact that the toothed rack is not driven with a spur wheel but rather with an intermediate wheel which is supported, in addition to the axle on which it is fastened on the worm on the shaft of the electric motor. The shaft is mounted in the electric motor, on the one hand, and, on the other hand, in a limiting means which simultaneously limits the tooth play with respect to the toothed rack and any axial play of the worm. The use of just a single toothed rack has the advantage, in particular, that even in the event of a change in direction, a high positioning accuracy is achieved with a high speed since a delay based on resiliently braced toothed racks does not occur. The drive system is self-locking. Self-locking is to be understood to mean the case where the frictional resistance in the gearing suffices to make it impossible for the worm to be driven by the worm wheel, which is formed by the intermediate gearwheel in this case. The drive system requires little outlay on account of the reduced number of gearwheels, and enables a short access time to different points on the recording medium by virtue of a high positioning accuracy and speed.